Abstract
Purpose: :
Photoreception is mediated by outer-retinal rod and cone photoreceptors, and melanopsin-expressing retinal ganglion cells. Gnat1-/- Cng3a-/- Opn4-/- (triple knock-out) mice lack critical elements of the phototransduction cascades associated with each of these mechanisms, via specific ablation of the rod transducin alpha-subunit, cone cyclic nucleotide gated channel, and melanopsin gene. Although assumed blind, these mice retain a small, transient pupillary light reflex. This led us to investigate whether other visual responses are also retained in this genotype and, if so, what photoreceptor drives them.
Methods: :
Flash ERGs were recorded from wild type and triple knock-out mice under dark adapted conditions and against a rod-saturating background light (2.6 log10 µW.cm-2). Light-dependent changes in spike-firing rate were assessed via multi-electrode recordings in the pretectum and thalamus of anaesthetised triple knock-out mice.
Results: :
We report a low amplitude but highly reproducible flash ERG in triple knock-out mice, indicating relatively widespread light-evoked activity in retinal neurons. This response originates in the outer retina, and has a spectral sensitivity matching that of rod opsin. In vivo recordings of neurons within retino-recipient areas also reveal light-evoked increases in firing rate.
Conclusions: :
Here we have identified an array of visual responses downstream of an α-transducin independent mechanism of phototransduction that is active in rod photoreceptors.
Keywords: photoreceptors • electroretinography: non-clinical • electrophysiology: non-clinical